Washington — Flip through any list of Republicans running for president or probably running or maybe thinking of running, and you'll find at least a couple dozen names. From Mitt Romney and Tim Pawlenty to Michele Bachmann, Rudy Giuliani, and Donald Trump, it's a potentially vast field peppered with outsize personalities and also folks who make you say, "who?"

Why so many?

"Because people perceive vulnerability in President Obama," says Darrell West, a political analyst at the Brookings Institution. "We have high unemployment, we have 2-1/2 wars, and there's a lot of contentiousness surrounding health care. So nobody's afraid to take on a sitting president."

By the time the Iowa caucuses roll around early next year, the GOP could easily field 10 to 12 candidates. The latest to say “I’m in” is Congresswoman Bachmann of Minnesota, a tea party firebrand and born-again Christian who could shake up the race by doing well in her native Iowa. She stole the show at last weekend’s Conservative Principles Conference in Iowa.

But it’s easy to see how a Bachmann candidacy fades in early states that are less friendly to evangelicals, such as New Hampshire, Nevada, and Florida. When all is said and done, the race for the 2012 GOP nomination may boil down to just three serious contenders: former Governor Romney of Massachusetts, former Governor Pawlenty of Minnesota, and Gov. Haley Barbour of Mississippi. Pawlenty announced his exploratory committee on March 20; Romney and Governor Barbour are expected to do so within the next several weeks.

For months, all three have been assembling campaign-level staffs, raising money for their political-action committees, traveling to early primary states, and building goodwill among local politicians and party activists. Former House Speaker Newt Gingrich, who is also clearly preparing to run, might have squeaked into the top tier if he hadn't botched his rollout in early March. Mixed signals from aides revived all the old stories of Mr. Gingrich's organizational shortcomings from his days as speaker.

The rest of the crowd

And what of all the other possible candidates? Many begin as long shots, and are likely to stay there – people like Herman Cain, the former CEO of Godfather's Pizza and the only African-American in the GOP field, and Buddy Roemer, the former Democratic governor of Louisiana who became a Republican in 1991. Both have launched exploratory committees but are not generating buzz. Gary Johnson, the libertarian-leaning former governor of New Mexico, is reportedly set to bypass an exploratory committee and announce his presidential candidacy in late April. Former Sen. Rick Santorum of Pennsylvania also looks to be running, but it's hard to see how he breaks out of the pack.

Three others could enter the top tier if they run, but for now, the signs point to their sitting this one out:

• Mitch Daniels. As Indiana governor, he has made a name for himself as a budget cutter and gave a highly regarded keynote speech on fiscal responsibility at the Conservative Political Action Conference in February. He has said he's thinking of running, and just inked a deal to write a book on limited government due out in September, but compromises with Democrats in the Indiana legislature could hurt Daniels’s chances with GOP primary voters.

•Sarah Palin. Perhaps more than anyone else, the former Alaska governor has the star power and fundraising skill to stir up the field. Recent trips to India and Israel boost her foreign-policy portfolio. But, like Gingrich, she has organizational problems and has shown little evidence that she's serious about running. Plus, now that Bachmann is “in,” Palin would face competition for the same pool of voters.

• Mike Huckabee. The former Arkansas governor has stellar communication skills but admits he's bad at fundraising. After a respectable run four years ago, it's not clear he has the fire in the belly to try again. And recent remarks about Mr. Obama's "childhood in Kenya," which he then disavowed, raise questions about his ability to appeal to a broad electorate.

Among the top three guys who are running, each has pluses and minuses. Romney is the only one to have run before, and that experience will be invaluable in a tough race. He can also draw upon personal wealth, which eases the fundraising pressure. But he has to answer for his Massachusetts health-care reform, the model for Obama's reform. And his Mormon faith still turns off many conservative evangelicals, a key part of the GOP base.

The ultimate insider

Barbour is the ultimate insider in the race, from his days as a respected national GOP chair and more recently chairman of the Republican Governors Association. Last fall he helped elect numerous Republican governors – many in critical battleground states – and they will owe him.

But his background as a lobbyist and as a born and bred Mississippian, with a syrup-thick accent, could hurt him. Recent statements on race have forced him into damage-control mode, an unfortunate place to be for one who aims to unseat the first black president. And in the end, Barbour’s candidacy could be a rerun of Phil Gramm’s in 1996, when the then-Texas senator spent $20 million in pursuit of the GOP nomination but did not even make it to the New Hampshire primary.

Pawlenty could wind up on top by default as the least objectionable. But that's hardly an endorsement for the grueling task of defeating an incumbent president. He is touting his fiscally conservative record as governor and his blue-collar background, but his demeanor is more "Minnesota nice" than Mr. Excitement.

Still, having governed a Democratic-leaning state for two terms, "he can argue that he can have some blue-state appeal – unlike, say, Haley Barbour," says Steven Schier, a political scientist at Carleton College in Northfield, Minn.

And a member of his inner circle, former Rep. Vin Weber (R) of Minnesota, insists that Pawlenty's newness to presidential politics won't hurt him, despite the GOP history of nominating people who have run before.

"I think the results of the last election convinced Republicans that they need to have fresh blood and new faces," says Mr. Weber.

Even if the GOP nomination race comes down to just Romney, Pawlenty, and Barbour, "it will still be a long, drawn-out process" when caucuses and primaries start early next year, says Ford O'Connell, chairman of the conservative CivicForumPAC. "Iowa could go Pawlenty, Bachmann, Barbour, 1, 2, 3. New Hampshire is Romney. South Carolina is Barbour."

But the field has hardly taken final shape. Mr. O'Connell suggests that those on the fence have until the Iowa Straw Poll on Aug. 13 to jump in. After that, it gets hard for candidates to find top-tier political talent available for hire. Former Governor Palin, in particular, can afford to wait, because of her fundraising skill. But she is polarizing, and even among conservatives, her appeal is waning.

A real game-changer would be New Jersey Gov. Chris Christie, whose blunt talk on fiscal matters has brought national notice. Governor Christie has been in office just over a year and insists he doesn't want to run for president, but in politics, never say never.